Leaky interface phonons in AlxGa1-xAs/GaAs structures

A dispersion equation for interface waves is derived for the interface of two cubic crystals in the plane perpendicular to [001]. A reasonable hypothesis is made about the total number of acoustic modes. According to this hypothesis the number is 64, but not all of the modes have the physical meaning of interface waves. Rules have been worked out to select physical branches among all 64 roots of the dispersion equation. The physical meaning of leaky interface waves is discussed. The calculations were made for the interface Al_0.3Ga_0.7As/GaAs. In this case all physical interface modes have been shown to be leaky. The velocities of the interface waves are calculated as functions of an angle in the plane of the interface. The results support a recent interpretation of weakfield magnetoresistance oscillations as a resonant scattering of a two-dimensional electron gas by the leaky interface phonons.